Periodic time-synchronous receivers are implemented in wide variety of modern electronic systems including wired and wireless voice and data communication systems, sensors for scientific, industrial, and consumer device use, and instrumentation for scientific, medical, and industrial use. Periodic time-synchronous receivers can be any one of a number of different types of synchronous/coherent receivers including, for example, receivers employed in sigma-delta A/D converters, receivers employed in communication systems (e.g., general radio receivers, radiotelephone receivers, micropower impulse radar receivers, aircraft communication receivers, fiber optic communication receivers, Ultra Wideband RF receivers, and the like), receivers employed in instrumentation systems (e.g., RF SQUID magnetometers, electrical impedance tomography, and the like), receivers employed in sensor systems (e.g., infrared sensing systems, vibratory MEMS Gyroscopes and the like), and the like.
One particular example of a periodic time-synchronous receiver is a capacitive touchsensing receiver employed in a capacitive sensing system that is used in conjunction with capacitive touchscreen. Capacitive touchscreens implement capacitive sensor technology to detect proximity or position on an object to the touchscreen based on capacitive coupling effects. Because capacitive touchscreen receivers measure very small changes in sensor line to device ground coupling capacitance, and/or very small changes in row to column coupling capacitance, capacitive touchscreen receivers are susceptible to external noise caused by a wide variety of noise sources including, but not limited to capacitively-coupled noise from the LCD implemented beneath the touchscreen, “floating” power supplies, external battery chargers, etc. Such receivers are susceptible to noise at their fundamental measurement frequencies as well as their harmonic, sub-harmonic and/or intra-harmonic frequencies.
Existing methods for noise reduction utilize shielding, frequency hopping, spread spectrum, pre-selection filtering and/or signal amplification to try and reduce and effectively eliminate the noise at the fundamental frequency and its harmonics. However, in some applications, resources such as computing resources, power supplies (i.e., batteries) and physical space can be very limited which can make it difficult or impossible to implement these methods.
Accordingly, it is desirable to provide improved methods and apparatus for reducing, suppressing and/or canceling noise and its effects at a periodic time-synchronous receiver such as a capacitive touchscreen receiver. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.